1. Field of the Invention
This invention relates to a radiating oscillator apparatus for micro- and millimeter waves that integrates electromagnetic wave radiation antenna and high-frequency wave oscillation capabilities, is usable in high-efficiency microwave submillimeter-region telecommunication apparatus and radiometry technologies, and incorporates spatial power combining for high-power output.
2. Description of the Prior Art
Conventional radio equipment, including widely-used radio communication apparatuses and different types of radiometry equipment such as radar systems and radiometers, is configured by combining antenna apparatus technologies and transmitter/receiver technologies related mainly to high-frequency circuitry. Antenna apparatus technologies for efficiently radiating electromagnetic waves and receiving electromagnetic wave signals according the intended purpose and high-frequency circuit technologies for the transmitters and receivers that handle signal processing and control have long constituted mutually independent fields of technology. They meet only in the need to match the antenna input and circuit output impedances.
The telecommunications equipment technology sector is seeing sweeping changes. Recent advances in semiconductor device technology have led to the development of technologies enabling amplifier, oscillator, multiplier, mixing and other high-frequency circuit element functions to be achieved by integrated planar circuits. These high-frequency integrated circuit technologies are widely looked to as providing next-generation radio communication apparatus technologies for achieving apparatuses whose integrated planar circuitry makes them simultaneously compact, light, highly performable, highly reliable and inexpensive. As such, they can be expected to obviate the conventional system of configuring apparatuses by interconnecting waveguide and coaxial circuit components. This evolving technology environment is creating a need for the development of new micro- and millimeter wave technologies that can integrate the antenna with the IC. The progress in high-frequency circuit semiconductor device technology has generated demand for a broad range of technologies. Among these are technologies that can provide the new device functions needed to configure micro- and millimeter wave mobile communications systems. Also needed are technologies for providing radiometry control systems with new capabilities, such as high-performance antenna beam shaping techniques and micro- and millimeter wave imaging techniques.
As frequency rises in the micro- to millimeter wave region, dielectric loss and conductor loss at the conductor surface increase to pose a major problem in terms of transmission line loss. Regarding antenna gain enhancement by arraying a planar antenna, this means both heavy feeder loss and a large drop in system total performance and efficiency owing to the connection through the long transmission line in the micro- and millimeter wave radio apparatus. Development of a new technology for integrating the antenna and the high-frequency planar circuit is therefore much needed. For this, however, numerous difficult technical problems will have to be solved.
In the simplest configuration, with the active circuit and the antenna circuit disposed adjacently on the same plane, it is difficult with high-frequency coupling to realize the desired apparatus performance by the antenna pattern, oscillator frequency, discrepancy of noise characteristics and the like. While rigorous consideration of spatial intercoupling methods is required in such cases, these are generally complex and, except in special cases, usually difficult to solve by electromagnetic field analysis.
As is clear from the foregoing, realization of transmitter technologies enabling efficient high-frequency generation and output as well as impartation of objective-matched directionality for radiation in the required direction requires development of a new method for functionally integrating the oscillator circuit and the antenna with high efficiency. Insufficient level of the high-frequency signal intended for transmission to a desired location has conventionally been coped with by either increasing the output of the signal source or increasing the antenna gain.
Provided that a signal source can be easily obtained that has sufficiently high output to compensate for the drop in radiation efficiency caused by the feeder loss, a multi-element antenna array with a sharp antenna characteristic can be assembled. In fact, however, millimeter wave semiconductor devices are fabricated using ultrafine processing technologies to provide the fine geometry needed to secure high-frequency characteristics. Since the power that individual devices can handle therefore falls sharply with increasing frequency, the finding of ways to achieve adequate output in the millimeter wave region is an important topic of technical research.
Securing sufficiently large high-frequency output in the micro- and millimeter wave regions requires the establishment of a technology for efficiently generating high-frequency output from individual devices. It also requires development of a new power combining technology for efficiently synthesizing the high-frequency outputs obtained from individual devices. One promising technology for power combining in the millimeter wave region, where transmission line loss is a particular problem, is the quasi-optical spatial phase synthesis method.
York et al. have reported a technique for spatial power combining by integrating planar patches serving as both a resonator and an antenna with an amplifier device and extracting high-frequency power as spatial output (R. A. York and R. C. Compton, "Quasi-Optical Power Combining Using Mutually Synchronized Oscillator Arrays", IEEE Trans. on Microwave Theory and Tech., Vol. MTT-39, pp. 1000-1009, 1991). They report on use of a two-terminal device (a Gunn diode) and a three-terminal device.
Matsui, one of the inventors of this invention, and coworkers have reported an effective method that combines antenna capability enabling efficient radiation of electromagnetic waves into space and resonator capability for configuring an oscillator integrated with a negative resistance amplifier circuit (U.S. Pat. No. 5,450,040). This method uses a Fabry-Perot resonator composed of spherical mirrors. The portion that couples with space forms a partially transparent, high-reflectance mirror surface and the other reflecting mirror surface is provided with a portion that couples with a negative resistance amplifier circuit and constitutes part of the conductor reflecting mirror surface thereof. By making this coupling relatively strong compared with that on the side coupled with space, high-frequency energy is accumulated inside the quasi-optical resonator to obtain a function as an antenna that leaks out the interior electromagnetic field of Gaussian distribution formed about the optical axis during steady state. As a result, use as a low sidelobe beam output oscillator apparatus is possible.
This beam output oscillator apparatus using a Gaussian beam resonator provides a number of outstanding features. One of these is a degree of freedom in determining the balance between high-frequency spectral purity and high-frequency output efficiency, which can be adjusted by selecting the combination between the coupling state of the resonator/antenna with space and the strength of the coupling between the resonator and the amplifier device. Another is the possibility of constituting the resonator portion of quartz, which has a low temperature coefficient and small loss, to obtain a high Q value that ensures simultaneous realization of high spectral purity and frequency stability and thus enables extraction of a good quality beam.
On the other hand, the Gaussian beam resonator is limited in application owing to its aperture of several wavelengths. Moreover, it is by nature a high-Q resonator and, as such, is not appropriate for use in wideband frequency modulation, multifrequency sharing and other such applications. Further, although suitable for overlaying with a planar circuit, a resonator shaped like a plano-convex lens with a spherical mirror on one side is relatively high in cost and a new solution is required from the aspect of cost reduction.
The technologies described in the foregoing have been unable to provide an oscillator apparatus capable of simultaneously achieving high frequency output with high efficiency and wideband characteristics from microwave to the still higher frequency millimeter wave region, high gain through array layout, and enhanced freedom of response to the need for higher output.
The present invention was accomplished in the light of the foregoing circumstances and has as an object to provide an oscillator apparatus for micro- and millimeter waves that constitutes an oscillator by integrating a resonator of planar structure and an amplifier device, simultaneously provides the resonator with the additional capability of a radiator for radiating electromagnetic waves into space, and enables high-frequency output to be extracted into space at high efficiency.
Another object of the invention is to provide an oscillator apparatus for micro- and millimeter waves suitable for implementing high-efficiency power combining.